The contest between John McCain and Mitt Romney has long resembled a horror movie, a blood-and-guts battle between a man risen from the dead and a candidate seemingly created in a lab. On Tuesday, a resurrected McCain slipped beyond the moneyed Michigan native's manicured grasp to win by five points in the Florida Republican primary and cement his status as the G.O.P. front-runner. Romney smiled through a thinly revised version of his ritual stump speech, as though the race hadn't fundamentally changed. But one could imagine what he might be thinking in the darker recesses of his mind: "Why won't you die?!"

McCain's victory tonight was his most significant yet, even if it was the ugliest. Most importantly, it was a win among Republicans and only Republicans; unlike New Hampshire or Iowa, there was no "independents' safety net," as a Romney staffer put it. A victory in Florida's closed primary should silence the refrain that has echoed through talk radio and conservative blogs ever since McCain started to claw his way toward the nomination: He's not a "real Republican." Says one McCain staffer: "Maybe after they see his name next to an 'R' in the general election they'll change their minds."

After his win in New Hampshire, critics proclaimed McCain too moderate to win over enough religious conservatives in South Carolina. After his victory there, critics insisted that Romney's millions, superior get-out-the-vote effort, and command of economic issues would erase the slim lead McCain had eked out in Florida. The day after Tuesday's convincing win, McCain's enemies will surely be looking for new ways to frame these same familiar complaints. But a look at the exit polls suggests that many of the assumptions that made McCain's candidacy look shaky from afar have dissolved in the heat of a competitive race.

For all of Romney's private-sector experience, McCain's almost quaint message of fiscal conservatism  he repeats the line "If only we could cut spending" to the point of parody  resonated among the many voters who were looking for answers to Florida's economic slump. Fifty percent of those who turned out Tuesday said that the economy was their most important issue, and McCain won those voters by 38% to 35%. Explains Steve Schmidt, a senior McCain adviser, "People understand the difference between a very good salesman and a commander in chief."

McCain does have real obstacles in his race to the nomination. His embrace of comprehensive immigration reform still rankles some; Romney got better than twice the support of voters for whom that was the number one issue. A new group, Citizens United Political Victory Fund, will start airing ads on Thursday that attempt to take up the "McCain is a liberal" theme anew. And Romney's big advantage cannot be discounted: "There's still a huge number of states to go," says unaligned G.O.P. pollster Whit Ayers. "And Romney has a lot more money."

Indeed, Romney outspent McCain in Florida on the order of eight to one. But he still lost, which is an encouraging sign for McCain. What's more, the money should now start rolling in to a McCain campaign that almost ended last summer over concerns about lackluster fund raising and overconfident spending. After months of forced modesty  in both hotel accommodations and attitude  McCain supporters are grinning again. "Rats are starting to leave multiple sinking ships," says one McCain fund raiser. "And all that money on the sidelines, who were just looking for an excuse to stay out. they don't have any excuses."

McCain can also expect to attract more endorsements in the days ahead. Up until now, his list of endorsements has been split between party elders like Phil Gramm and Howard Baker and newspaper editorial pages. (Aides sometimes refer to their boss as "president of the ed boards.") On Wednesday in California, Rudy Giuliani is widely expected to bow out of his candidacy and endorse McCain, his old friend.

Those who will continue to search for reasons why McCain can't win the Republican nomination are starting to resemble that skeptical bit character in horror films  the one who refuses to believe that the monster is real. He's the one, it should be pointed out, who usually gets killed first.